Summary

Description

Flat or fleshy colonies with zooids 2-4 mm across arranged in conspicuous star shaped systems, each with a central cloacal opening. Colonies vary greatly in colour including green, violet, brown and yellow.

Recorded distribution in Britain and Ireland

Found all around Britain and Ireland

Global distribution

Present from the Faeroe Islands and west and south Norway to the Mediterranean including the Adriatic and Black Seas. Also present in the western Atlantic from Maine to New Jersey and in Florida.

Habitat

Grows on a variety of stable substrata including algae and artificial substrata. Thrives in sheltered areas including docks. Although mainly found on the lower shore and in shallow depths, Berrill (1950) notes that it has been found at depths of several hundred metres.

This MarLIN sensitivity assessment has been superseded by the MarESA approach to sensitivity assessment. MarLIN assessments used an approach that has now been modified to reflect the most recent conservation imperatives and terminology and are due to be updated by 2016/17.

Physical pressures

Botryllus schlosseri is a sessile species dependant on the continued presence of the substratum to which it is attached. Removal of the substratum would remove the species. However, providing that suitable substratum remains after disturbance, settlement and growth from larvae is high.

Botryllus schlosseri occurs in areas where high levels of smothering due to siltation may occur but is generally found where silt is unlikely to settle (down-facing or suspended surfaces) suggesting that it is intolerant of smothering. Smothering may prevent feeding and respiratory flows through the colony and the species may not survive burial. However, providing that suitable substratum is available after the smothering event is over, settlement and growth from larvae is high.

Botryllus schlosseri occurs in areas where high levels of siltation and smothering may occur but is generally found where silt is unlikely to settle (down-facing or suspended surfaces) suggesting that it is intolerant of siltation. Silt may clog feeding and respiratory flows through the colony. However, providing that suitable substratum is available, settlement and growth from larvae is high.

Botryllus schlosseri occurs only in shaded areas on the lower shore in the intertidal where the atmosphere remains damp. Exposure to air and sunshine (for instance if boulders with colonies are overturned) would be likely to destroy colonies. However, providing that suitable substratum is available after a desiccation event, settlement and growth from larvae is high.

Botryllus schlosseri occurs only in shaded areas on the lower shore in the intertidal where the atmosphere remains damp. Increased exposure to air would be likely to destroy colonies. However, providing that suitable substratum is available after a emergence event, settlement and growth from larvae is high.

Water flow rate is important for maintaining colonies free of silt where they occur in sheltered areas. If water flow rate is decreased in such areas, and siltation occurs, colonies are likely to be adversely affected. However, once a high water flow rate is regained, settlement and growth from larvae is high.

Botryllus schlosserioccurs from sub-arctic to warm temperate conditions and most likely tolerates a wide range of temperatures. Recolonization of suitable substrata would be rapid following once temperatures return to normal.

Botryllus schlosserioccurs in areas where high levels of turbidity occur although, as a passive suspension feeder, it may be susceptible to clogging (see siltation above). Increased turbidity may decrease phytoplankton productivity which may indirectly decrease food availability. Recolonization of suitable substrata would be rapid once turbidity returned to normal.

Increase in wave exposure or storm events would remove predominantly the plants on which Botryllus schlosseri grows and therefore incidentally Botryllus schlosseri. Speed of recovery would depend on regrowth rates of the plant substrata.

Abrasion from sand is likely to be tolerated and Botryllus schlosseri occurs attached to algae on surf beaches. However, abrasion caused by mobile hard substrata, and anchor or dredge, is likely to remove colonies. Recolonization of suitable substrata would be rapid following cessation of abrasion.

Botryllus schlosseri is permanently attached to the substratum and displacement is likely to have the same effect as substratum loss. Speed of recolonization would depend on the presence of suitable substrata.

Botryllus schlosseri lives in enclosed waters including docks and in estuaries where salinity is variable. However, its absence from low salinity conditions in upper estuaries and lagoons suggests that colonies will be intolerant of low salinities. Recolonization following cessation of exposure to low salinity is likely to be rapid.

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